Perpendicular magnetic recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole layer with a small surface area at an air bearing surface (ABS), and coils that conduct a current and generate a magnetic flux in the main pole such that the magnetic flux exits through a write pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a selected number of bits in the magnetic medium and typically returns to the main pole through two pathways including a trailing loop and a leading loop. The trailing loop has a trailing shield structure with first and second trailing shield sides at the ABS. The second (PP3) trailing shield arches over the write coils and connects to a top yoke that adjoins a top surface of the main pole layer near a back gap connection. The leading loop includes a leading shield with a side at the ABS and that is connected to a return path (RTP) proximate to the ABS. The RTP extends to the back gap connection (BGC) and enables magnetic flux in the leading loop pathway to return from the leading shield at the ABS and through the BGC to the main pole layer. A PMR head has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density.
The double write shield (DWS) design that features the leading and trailing loops was invented for adjacent track erasure (ATE) improvement by reducing stray field in side shields and in the leading shield. Magnetic flux is able to flow evenly through the leading loop and trailing loop. In the trailing loop, there is a hot seed (HS) layer that is a magnetic layer with high saturation magnetization from 19 to 24 kG formed between a top surface of the write gap and a bottom surface of the first trailing shield at the ABS. A good HS response is required to reduce stray fields in the side shields and leading shield.
Perpendicular magnetic recording has become the mainstream technology for disk drive applications beyond 150 Gbit/in2. With the growing demand for cloud storage and cloud-based network computing, high and ultra high data rate recording becomes important for high-end disk drive applications. Thus, it is essential to design a PMR writer that can achieve high area density capability (ADC) in addition to improved stray field robustness characterized by low ATE and a bit error rate (BER) of about 10−6.
In today's PMR heads, the critical dimensions (CDs) of the PMR writer such as the track width (TW) are within a 10 nm to 100 nm range. However, the capabilities of process tools and variations in writer CDs have not been keeping up with the reductions in CDs. As a result, there are typically large fluctuations in writer performance, which impact both HGA yield and subsequent HDD yield. Thus, there is a need for an improved PMR writer design that minimizes variations in writer performance without having adverse thermal-mechanical implications or system level integrations issues.